i965: Respect stride and subreg_offset for ATTR registers

i965: Respect stride and subreg_offset for ATTR registers

When we assign hw regs to attributes, we don't incorporate the stride
and subreg_offset from the fs_reg. It's rarely used, but the integer
multiplication lowering uses unusual stride and subreg_offset
combination breaks when one source is an attribute.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91970
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kristian Høgsberg Kristensen <krh@bitplanet.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>